What does Online Listings Column mean?

Online Listings Column shows the online listings to which this product is linked. A product can be linked to multiple listings if the SKU in those listings is common.

Example 

The first 2 products have 1 Online listing against them, while the 3rd one on the list has 3 listings against it. 

When you click on the number given in Online Listings column, it will open the details of the linked listings.